1. Field of the Invention
The present invention relates to a fuel cell system and a control method thereof. In more detail, the present invention relates to a fuel cell system that supplies a low flow rate of oxidizing gas and produces low current from the fuel cell during an idling stop, as well as a control method thereof.
2. Related Art
In recent years, fuel cell systems have received attention as a new source of power for automobiles. Fuel cell systems are provided with a fuel cell that generates power by allowing reactant gases to undergo an electrochemical reaction, and reactant gas supply devices that supplies reactant gases to the fuel cell via reactant gas channels, for example.
The fuel cell is a stack structure in which several tens to several hundreds of cells are stacked, for example. In this regard, each cell is configured by sandwiching a membrane electrolyte assembly (MEA) with a pair of separators. The membrane electrolyte assembly is configured by an anode and cathode, and a solid polymer electrolyte membrane sandwiched between these electrodes.
When hydrogen is supplied as fuel gas to the anode of the fuel cell, and air is supplied as oxidant gas to the cathode, an electrochemical reaction progresses to generate power. Fuel cells have been regarded as preferable in the aspect of high power generation efficiency since the fuel cell obtains electricity directly through an electrochemical reaction in this way. In addition, fuel cells have been regarded as preferable also in the aspect of the impact on the environment since only harmless water is produced during power generation.
However, in fuel cell vehicles with such a fuel cell system as the source of power, in a case of idling power generation being continuously carried out when the vehicle is stopped such as when waiting at a traffic signal, for example, idling stop to stop idling power generation is executed by stopping the supply of oxidant gas and fuel gas. Efficient use of fuel is made possible by executing this idling stop.
However, when executing this idling stop, the fuel cell becomes high potential due to the power generation from hydrogen and oxygen remaining inside the fuel cell system, and the electrolyte membrane may degrade. Therefore, a technology has been proposed for preventing the hydrogen and oxygen remaining inside the fuel cell system from being consumed by producing current from the fuel cell, and the fuel cell becoming high potential, along with suppressing degradation of the electrolyte membrane, even in a case of stopping the supplies of oxidant gas and fuel gas during idling stop (e.g., refer to Patent Document 1).
In addition, when executing idling stop, the hydrogen and oxygen staying in the vicinity of the electrolyte membrane during the occurrence of the cross-leakage phenomenon or the like will react at high concentrations, and the electrolyte membrane may degrade. Therefore, technology has been proposed to decrease the oxygen amount staying in the vicinity of the electrolyte membrane to suppress reaction with hydrogen by supplying oxidant gas of a low flow rate to the fuel cell during idling stop, thereby suppressing degradation of the electrolyte membrane (e.g., refer to Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-294304    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2005-327492